Self-regulated battery charger



May 23, 1967 i R. WALSH 'SELF-REGULATED BATTERY CHARGER Filed Jan. 10,1963 INVENTOR Robert R. Walsh ATTORNEY United States Patent Ofiice3,321,691 Patented May 23, 1967 3,321,691 SELF-REGULATEID BATTERYCHARGER Robert R. Walsh, Wilmington, Del., assignor to All AmericanEngineering Company, Wilmington, Del., a corporation of Delaware FiledJan. 10, 1963, Ser. No. 250,624 2 Claims. (Cl. 320-40) For example, atypical silvercell might require a charging current of 200 milliamperesapplied thereto until the terminal voltage of the cell reaches 2.02volts. Upon reaching this exact terminal voltage the charging currentmust be immediately discontinued or damage to the cell will result.

Thus, for batteries of this type, charging operations require carefulcontinuous monitoring during the charging cycle and the attendantinstrumentation must be of a high sensitivity not commonly found outsideof laboratories and other commercial electronic establishments.

It is, therefore, an object of this invention to provide an inexpensiveandhighly sensitive battery charger including automatic battery terminalvoltage monitoring means which automatically terminates the chargingcycle of a battery upon the advent of rated terminal voltage at saidbattery. 7

Another object of this invention is to provide an-inexpensive and highlysensitive battery charger having a first charging circuit includingautomatic battery terminal voltage monitoring means which automaticallyterminates the charging operation of said first circuit upon the adventof rated terminal at the battery under charge, and second circuit meanscomprising means for continuously trickle charging said battery.

Still another object of this invention is to provide an inexpensive andhighly sensitive battery charger including automatic battery terminalvoltage monitoring means which automatically terminates the chargingcycle of a battery upon the advent of rated terminal voltage at saidbattery, said monitoring means including, as a control element, asilicon controlled semi-conductor switching means.

These and other objects of this invention will become more fullyapparent with reference to the following specifieation and drawingswhich relates to several preferred embodiments of the invention.

In the drawings:

FIGURE 1 is a schematic diagram of a first embodiment of a batterycharger under the present invention;

FIGURE 2 is a schematic diagram of a second embodiment of a batterycharger under the present invention and comprises the embodiment ofFIGURE 1 combined with a trickle charging means.

Referring in detail to the drawings and more particularly to FIGURE 1, afirst embodiment of the battery charger of the invention is shown asincluding an input transformer T having a primary winding 10 and asecondary winding 12, the primary 10 being connected in series with anon-oif switch 14 and a fuse 16 and adapted to be connected across anysuitable alternating current supply by means of a power plug 18.

The secondary 12, of the transformer T, includes first and second outputterminals 20 and 22, respectively, across which is connected a rectifierdiode D in series with a filter capacitor C the anode of the diode Dbeing connected with the first output terminal 20. The cathode of thediode D and one terminal of the filter capacitor C are connected at acommon node 24.

The second output terminal 22 of the secondary 12 is connected through acommon lead 26 directly to the negative output terminal 28 of thebattery charger.

The first output terminal 20 of the secondary 12 is connected, via aseries circuit comprising a current limiting resistor R anode terminal30 and cathode terminal 32 of a silicon controlled rectifier or threeterminal switch SCR and a fuse 34, with the positive output terminal 36of the battery charger.

A voltage standard is provided by means of a voltage divider comprisingfirst and second series connected dropping resistors R and Rrespectively, connected from the node 24 between the rectifier diode Dand filter capacitor C to the common lead 26 and having a common node 38therebetween which is also connected to the common lead 26 via a Zenerdiode D The Zener diode D is thus in parallel with the second droppingresistor R The second dropping resistor R is provided with a sliding tap40 which is connected directly to the gate or control terminal 42 of thesilicon controlled rectifier SCR via a lead 44. However, for highervoltage applications wherein large control currents might result, asuitable current limiting resistor may be placed in series with the tap40 and gate terminal 42.

Referring now to FIGURE 2, a second embodiment of the invention is shownwhich includes the identical circuit as shown in FIGURE 1, likecomponents being indicated by like numerals, coupled with a tricklecharging circuit comprising a series connected current limiting resistorR;

and a rectifying diode D connected between the first output terminal 20of the transformer secondary 12 and a node 46 located between thecathode terminal of the controlled rectifier SCR and the fuse 34.

Operation Referring to FIGURE 1, the rectifying diode D and filtercapacitor C rectify the output of the transformer secondary 12 anddeliver direct current power to the common node 24 therebetween,creating a voltage drop across the voltage divider dropping resistors Rand R The rela tive values of the said resistors R and R are such thatthe Zener diode will break down and conduct in the reverse direction inresponse to the initial voltage appearing at the node 38 therebetweenand across the second dropping resistor R whereby thereafter, aregulated standard voltage appears across the said second droppingresistor R By selectively adjusting the position of the slide 40 alongthe second dropping resistor R the gating voltage applied via the lead44 to the gate terminal 42 of the controlled rectifier SCR isconstrained to the proper value with respect to the particularconditions of operation.

A battery, not shown, is connected in charging position across theoutput terminals 36 and 28 and the gating voltage at the gate terminal42 is adjusted via theslide 40 such that the minimum forward biaspotential from gate terminal 42 to the cathode terminal 32 is equal tothe diiference between the gating voltage and the maximum rated terminalvoltage of the battery being charged, this latter voltage being thatappearing at the positive output terminal 36 when the battery is fullycharged.

Since it is characteristic of silicon controlled switch ing devices thatthey will not conduct except when a small control current determined bya forward bias or gating potential is flowing in a forward directioninto the gating terminal thereof, the silicon controlled switching meansSCR will be biased to cut off and effectively appear to be an opencircuited switch when the potential difference between the gatingvoltage at the gate terminal 42 and the voltage at the cathode terminal32, the latter in this case being the terminal voltage of the batterybeing charged, drops below a predetermined minimum for the particulartype silicon controlled switching device used. For example, a siliconcontrolled switch such as a G. E. Type CSU or a silicon controlledrectifier such as a G. E. Type C15U may be used as the siliconcontrolled switch means SCR in the present invention.

Referring now to FIGURE 2, whereinthe operating of the automatic portionof the circuit shown is identical with that of FIGURE 1, the tricklecharging circuit comprising the limiting resistor R and the rectifyingdiode D act to continually supply a small trickle of direct current to abattery, not shown, connected across the output terminals 28 and 36 ofthe charger.

It will be apparent that methods known in the art can be applied forcompensating the various components of this circuit against thermaldrift of characteristics resulting from changes in ambient temperaturesshould such additional stability be required.

As can be seen from the foregoing specification and drawings, thisinvention provides a battery charger which is inexpensive, compact andhighly sensitive and which automatically monitors the terminal voltageof a battery being charged thereby and automatically terminates thecharge cycle upon the advent of rated or other predetermined terminalvoltage at the said battery. There is also provided an embodiment of theinvention which additionally provides a trickle charge for that type ofbatteries connected with the battery charger wherein the trickle chargeis needed to prevent chemical deterioration therein. Additionally thepresent invention provides a battery charging. means whereby silvercellbatteries and the like may be more widely used commercially.

It is to be understood, that the embodiments of the invention shown anddescribed herein are for the purpose of example only and are notintended to limit the scope of the appended claims.

What is claimed is:

1. Charging means for delivering charging current to a load, said loadhaving a predetermined rated terminal voltage in a fully chargedcondition and a lesser terminal voltage when in a discharged condition,said charging means comprising a power source, circuit means connectedwith said power source for deriving a voltage standard therefrom,silicon controlled rectifier means connected in series with said powersource and said load, said controlled rectifier means including a gateterminal, and conductor means connecting said gate terminal with saidcircuit means whereby a bias potential is applied to said gate terminal,said bias potential being selected such that said controlled rectifiermeans will prevent the flow of charg- 7 ing current to said load uponthe advent of rated ter minal voltage at said load; wherein said circuitmeans comprises a filter capacitor and rectifier means connected inseries across said power source, a voltage divider comprising first andsecond series connected resistance means connected across said filtercapacitor, and a voltage regulator means connected across said secondresistance means, said second resistance means having a variable centertap thereon connected with said conductor means, whereby a selectivelyvariable bias potential is provided for said gate terminal of saidcontrolled rectifier means.

2. Charging means for delivering charging current to a load, said loadhaving a predetermined rated terminal voltage in a fully chargedcondition and a lesser terminal voltage when in a discharged condition,said charging means comprising a power source, circuit means connectedwith said power source for deriving a voltage standard therefrom,silicon controlled rectifier means connected in series with said powersource and said load, said controlled rectifier means including a gateterminal, and conductor means connecting said gate terminal with saidcircuit means whereby a bias potential is applied to said gate terminal,said bias potential being selected such that said controlled rectifiermeans will prevent the flow of charging current to said load upon theadvent of rated terminal voltage at said load; wherein said circuitmeans comprises a filter capacitor and rectifier means connected inseries across said power source, a voltage divider comprising first andsecond series connected resistance means connected across said filtercapacitor, and a voltage regulator means connected across said secondresistance means, said second resistance means having a variable centertap thereon connected with said conductor means, whereby a selectivelyvariable bias potential is provided for said gate terminal of saidcontrolled rectifier means; and wherein said controlled rectifier meansincludes anode and cathode terminals in series with said power sourceand said load, and wherein said bias potential is selected such that thepotential difference between said gate terminal and said cathode, whensaid load is fully charged to rated terminal voltage, is equal to theminimum forward bias required to cause said controlled rectifier meansto conduct.

References Cited by the Examiner UNITED STATES PATENTS 3,018,432 1/1962Palmer 323--22 3,160,805 12/1964 Lawson 320-39 3,164,764 1/1965 Marsalet a1. 320-53 3,176,210 3/1965 Bethke 320-40 JOHN F. COUCH, PrimaryExaminer.

R. C. SIMS, Examiner.

L. L. MCCOLLUM, G. H. GERSTMAN, S. WEIN- BERG, Assistant Examiners.

1. CHARGING MEANS FOR DELIVERING CHARGING CURRENT TO A LOAD, SAID LOADHAVING A PREDETERMINED RATED TERMINAL VOLTAGE IN A FULLY CHARGEDCONDITION AND A LESSER TERMINAL VOLTAGE WHEN IN A DISCHARGED CONDITION,SAID CHARGING MEANS COMPRISING A POWER SOURCE, CIRCUIT MEANS CONNECTEDWITH SAID POWER SOURCE FOR DERIVING A VOLTAGE STANDARD THEREFROM,SILICON CONTROLLED RECTIFIER MEANS CONNECTED IN SERIES WITH SAID POWERSOURCE AND SAID LOAD, SAID CONTROLLED RECTIFIER MEANS INCLUDING A GATETERMINAL, AND CONDUCTOR MEANS CONNECTING SAID GATE TERMINAL WITH SAIDCIRCUIT MEANS WHEREBY A BIAS POTENTIAL IS APPLIED TO SAID GATE TERMINAL,SAID BIAS POTENTIAL BEING SELECTED SUCH THAT SAID CONTROLLED RECTIFIERMEANS WILL PREVENT THE FLOW OF CHARGING CURRENT TO SAID LOAD UPON THEADVENT OF RATED TERMINAL VOLTAGE AT SAID LOAD; WHEREIN SAID CIRCUITMEANS COMPRISES A FILTER CAPACITOR AND RECTIFIER MEANS CONNECTED INSERIES ACROSS SAID POWER SOURCE, A VOLTAGE DIVIDER COMPRISING FIRST ANDSECOND SERIES CONNECTED RESISTANCE MEANS CONNECTED ACROSS SAID FILTERCAPACITOR, AND A VOLTAGE REGULATOR MEANS CONNECTED ACROSS SAID SECONDRESISTANCE MEANS, SAID SECOND RESISTANCE MEANS HAVING A VARIABLE CENTERTAP THEREIN CONNECTED WITH SAID CONDUCTOR MEANS, WHEREBY A SELECTIVELYVARIABLE BIAS POTENTIAL IS PROVIDED FOR SAID GATE TERMINAL OF SAIDCONTROLLED RECTIFIER MEANS.